1. Field of the Invention
The present invention relates to a head suspension mechanism which is used for a magnetic disc unit such as a hard disc mounted on a personal computer and elastically supports a head slider to perform recording and regenerating to a magnetic disc. More particularly, it relates to a head suspension mechanism with a dynamic vibration absorber, which is capable of restraining vibrations caused by an air flow generating due to the high-speed rotation of the magnetic disc, especially sway mode vibrations and second-order torsion mode vibrations that result in a positional shift between a head and a recording track.
2. Description of the Related Art
A personal computer and the like have conventionally used a magnetic disc unit as a recording/regenerating medium for information.
FIG. 12 is a plan view showing one example of a general magnetic disc unit. As shown in FIG. 12, the magnetic disc unit D is configured so that a magnetic disc body d capable of rotating at a high speed is held in a housing B consisting of a lid-shaped mating structure (only one is shown), and a head arm HA, which is capable of being rotated in a substantially radial direction (refer to an arrow mark) of the magnetic disc body d by the drive of a voice coil motor (VCM) M, is provided so as to face to the magnetic disc body d. Also, in a free end part of the head arm HA, there is provided a head slider suspension HS that holds a head slider (not shown) for performing writing of data to the magnetic disc body d and reading of the written data.
In recent years, the capacity and speed of the magnetic disc body d have increased. Accordingly, the head slider suspension HS is required to have vibration damping properties so as to prevent the occurrence of vibrations of head caused by an air flow (turbulent flow) generating when the magnetic disc body d rotates.
FIG. 13 is a perspective view of a head suspension, showing one example of a conventional head suspension mechanism. This head suspension 1 includes a fixed plate 2 stakingly connected to the aforementioned head arm HA, a suspension main frame 3 consisting of a thin metal sheet fixed to the fixed plate 2, a flexure 4 fixed at the tip end of the suspension main frame 3, and a head slider 5 fixed on the bottom surface at the tip end of the flexure 4.
In a base part of the suspension main frame 3, a leg portion 3a is formed so as to provide flexural elasticity by blanking a central part thereof. Also, at both edges of the suspension main frame 3, flange portions 3b erecting along the edges are formed.
In the flexure 4, a substantially U-shaped slit 4a is formed so as to surround a central part thereof, so that by elastically fixing the head slider 5, a load from the suspension main frame 3 is applied to a central part of the back surface (fixed surface) of the head slider 5.
Since the configuration is as described above, the head suspension mechanism supports the head slider 5 for performing recording/regenerating on the surface of the magnetic disc body d rigidly in the in-plane direction (horizontal direction=XY direction) and flexibly in the out-of-plane direction (vertical direction=Z direction), and also can perform a function of giving a fixed load force to the head slider 5.
Also, since the head suspension mechanism is moved in the in-plane direction at a high speed to move the head slider 5 to a recording track of the magnetic disc body d at a high speed, it is important that the suspension mechanism be as light in weight as possible and moreover be not subjected to vibrations as an elastic body.
For this reason, as shown in FIG. 13, the suspension main frame 3 is formed into a tapered triangular shape by using a stainless steel material with a thickness of several tens of micrometers, and the flange portions 3b erecting vertically are formed at both edges of the suspension main frame 3, by which the suspension main frame 3 itself is configured so as to be light in weight and have high flexural rigidity. The flexible flexural elasticity function of the head suspension mechanism is provided in the leg portion 3a for fixing the suspension main frame 3 to the fixed plate 2.
Since the head slider 5 is fixed to the flexure 4, the head slider 5 is supported flexibly not only in the out-of-plane direction but also the pitching direction and the rolling direction so as to follow the vibrations and swell of the magnetic disc surface by means of air film rigidity.
FIG. 14 is a perspective view of a head suspension, showing another example of the conventional head suspension mechanism. In this head suspension, the thickness of the suspension main frame 13 is increased as a whole, by which the flange portions 3b of the suspension main frame 3 are eliminated. In FIG. 14, the same reference characters are applied to elements that are substantially the same as those in FIG. 13, and the explanation thereof is omitted.
In recent years, the density of track recorded on the magnetic disc surface has been becoming high. Accordingly, an air flow around the suspension, which is generated by the rotation of the magnetic disc body d, induces minute elastic vibrations on the order of nanometers, which becomes a main cause for a track positioning error of the head slider 5.
Such an elastic vibration has many components having a frequency higher than a servo band, and hence cannot be restrained by control, so that an excitation vibration itself must be reduced. Therefore, it is considered that as shown in FIG. 15, a restraining multilayer visco-elastic plate 6 is affixed to the upper surface of the suspension main frame 3 to provide damping.
This restraining multilayer visco-elastic plate 6 is formed into a multilayer structure in which the upper layer is a restraining metal plate 6a and the lower layer is a visco-elastic material 6b, and has a construction such that the visco-elastic material 6b is held between two metal plates of the suspension main frame 3 and the restraining metal plate 6a. 
The restraining multilayer visco-elastic plate 6 produces a damping force by means of relative motion between the visco-elastic material 6b and the upper and lower metal plates, so that an effect of damping flexural vibrations of the suspension mechanism is great. However, the restraining multilayer visco-elastic plate 6 has a problem in that an effect of damping torsional vibrations and sway mode vibrations in which the tip end of suspension vibrates swingingly in a plane is little.
The sway mode vibration is a vibration of a mode in which the head slider 5 is vibrated in the track position shift direction (Y direction in FIG. 15), and is responsible for a shift of track of the head slider 5. Therefore, it is desirable to effectively damp the sway mode vibrations excited by an air flow.
The torsional vibrations can also be adjusted so as not to affect the track position sift and float clearance variation due to the first-order mode. However, the second-order torsion mode vibrations often produce a track shift.
Thereupon, it is considered that the sway mode and second-order torsion mode vibrations of the head suspension mechanism caused by an air flow are prevented (refer to U.S. Pat. No. 5,943,191).
FIG. 16 shows a head suspension showing an idea of applying a technique similar to the dynamic vibration absorber to the head suspension mechanism.
In the typical example shown in FIG. 16, a fixture 14 is provided with a mustache-shaped damping plate 14a, and a frictional force due to relative vibrations of a contact portion between the damping plate 14a and a contact plate 15 caused when the flexure 14 is going to vibrate is utilized.
Such measures are effective when the flexure 14 resonates greatly. However, the measures have a drawback in that no effect is achieved in the case of minute vibration in which the contact portion between the damping plate 14a and the contact plate 15 does not shift relatively.